1. Field of the Invention
This invention relates to a water-based ink composition, and an ink-jet recording process.
2. Description of the Related Art
As ink-jet recording systems, ink ejection systems are known in the art as exemplified by a system utilizing electrostatic attraction, a system in which mechanical vibration or displacement is imparted to an ink composition by the use of a piezoelectric device, and a system in which an ink composition is heated to cause it bubble and a pressure produced when it bubbles is utilized. Ink droplets are formed by some of these ink ejection systems, and part or the whole of the droplets is caused to adhere to recording mediums such as paper to make a record. When writing implements such as fountain pens, felt-tip pens and ball-point pens are used, an ink composition is ejected from capillaries and the ink composition thus ejected is received on recording mediums to make a record. As ink compositions used in such ink-jet recording systems or writing implements, those prepared by dissolving or dispersing a water-soluble dye or a pigment in water or an aqueous medium comprising water and a water-soluble organic solvent are known and put into use.
In such conventional ink compositions, they are of course required to have various performances. In particular, the performance most required is the liquid stability that the ink composition does not cause clogging of, and deposits at, nozzles or orifices of recording apparatus or pen points when recording is being performed using the ink composition, when the recording is paused and also when the recording is stopped over a long period of time. Especially in the ink-jet recording systems, the apparatus are expensive compared with the writing implements, and hence it is important to prevent ink-jet nozzles or orifices from clogging. Moreover, in the ink-jet recording systems, if the nozzles or orifices are not even clogged, faulty images due to curved jets, changes in ink drop quantity and changes in flying speed which are caused by the deposits formed at the nozzles or orifices have caused a great problem. Furthermore, among the ink-jet recording systems, the thermal ink-jet recording system that utilizes heat energy tends to cause deposition of foreign matter on the surface of a heating element as a result of temperature changes, and the problem is more important.
Commercially available dyes or pigments used as materials for ink compositions also contain many impurities (e.g., organic matter and inorganic matter such as dispersants and leveling agents). Ink components other than the dyes or pigments, as exemplified by water and water-soluble organic solvents, also contain not a little organic or inorganic impurities. Still also, during the manufacture of ink compositions, various impurities may be included therein according to containers or implements used and the environment.
Under such circumstances, it has been attempted to solve the above problems by controlling the quantity of the impurities in ink compositions that may cause the deposits.
For example, Japanese Patent Application Laid-open No. 3-48951 discloses a liquid composition containing a water-soluble dye used in ink-jet recording and in which iron and silicon contained therein are controlled to be in a content not more than 9 ppm in total. Japanese Patent Publication No. 2-2906 also discloses an ink-jet recording ink composition mainly composed of an aqueous solution containing a water-soluble acid dye or water-soluble direct dye having been subjected to ion exchange by the use of a cationic ion-exchange resin.
Japanese Patent Application Laid-open No. 64-4350 also discloses an ink-jet recording apparatus in which sodium ions in an ink composition are controlled to be in a content of 0.001% by weight to 0.2% by weight, and fatty acids and fatty acid derivatives contained in materials constituting an ink tank, 10 to 100 ppm in total weight.
Japanese Patent Publication No. 60-48552 still also discloses an ink composition comprising water, a water-soluble dye and a polyhydric alcohol or polyhydric alcohol derivative and in which a fatty acid ester as an anti-foaming agent is controlled to be in a content of 0.01% by weight to 5% by weight.
Such conventional impurity-controlled ink compositions are more improved than ink compositions containing impurities in excess. However, they have not necessarily been well effective when, for example, even the long-term storage of ink compositions and the changes in temperature and environment are taken into account. In particular, they have not perfectly solved the problems of the curved jets, changes in ink drop quantity and changes in flying speed in the ink-jet recording systems. In the case of the ink-jet recording system utilizing heat energy, they have been not able to well prevent the deposition of foreign matter on the heating element.
The above Japanese Patent Application Laid-open No. 64-4350 does not teach any control of the quantity of fatty acids or fatty acid esters in ink compositions.
The above Japanese Patent Publication No. 60-48552 teaches control of the quantity of a fatty acid ester intentionally added as an anti-foaming agent, but does not teach any control of the quantity of fatty acid esters as well as impurities that are actually present in ink compositions.